Armored cable construction



June 17, 1941. (:ARLSQNv 2,246,124

ARMORED CABLE CONSTRUCTION Filed Aug. 23, 1938 Fig.2.

Inventor; George .Carlson,

by Hi 5 Attorneg.

Patented June 17 1941 UNITED STATES PATENT OFFICE AaMoItEn CABLECONSTRUCTION York Application August 23, 1938, Serial No. 226,265

2 Claims. (Cl. I'M-109T This invention relates to an armored cableconstruction, and more particularly to a cable employing apaper wrap iricombination with a spiral metallic armor. The invention further relatesto an improved form of bushing for use with the cable in protecting thesevered end of the armor. Y

It is an object of the invention to provide an improved construction andarrangement in cable and bushing constructions of the type described,which possess improved electrical and mechani-, cal characteristics, andwhich may be manufactured at low cost.

In the accompanying drawing Fig. l is a view of an armored cable withthe bushing in operative position; Fig. 2 is a sectional view through acable employing two conductors showing the 'manner of applying theinsulating paper wrap;

Fig. 3 is a sectional view through a. modification of the cableemploying three conductors; Fig. l is a sectional view through anothermodification of the cable employing four conductors; Fig. 5 is aperspective view of the bushing for use with the cable, and Fig. 6 is adiagrammatic view of the twisted conductors and paper wrap.

Referring to thedrawing the numeral it] refers to the improved form ofarmored cable shown most clearly by Fig. 1. In the form of the inventionillustrated by Figs. 1 and 2 the cable employs two insulated conductorshaving conducting wires ll, each being insulated with a rubber compoundi2 and an overall saturated braid I 3. In the manufacture of the cablethe individual insulated conductors are run through a twisting machine,together with a longitudinal strip of waxed paper M, commonly known tothe trade as krait paper. Upon entering the twisting machine theindividual conductors are twisted together about the longitudinal paperas an axis so that the paper is wrapped about the individual conductorsin an S-iorm, as shown by Fig. 2. In this form a central portion of thepaper wrap remains placed between each of the insulated conductors, asshown at it, while the edges I 5 of the paper wrap encircle the entireperiphery of the insulated conductors and completely cover them. Asshown diagrammatically by Fig. 6, the edges of the d-shaped paper wrapappear twisted as they cover the twisted conductors. Inasmuch as thestrip of paper it is fed into the twisting machine longitudinally andthe conductors are twisted about the paper wrap, it will be apparentthat the. paper wrap constitutes in effect a longitudinal wrap runninglengthwise of the cable and having a length equal to the length of thecable. It will be seen that with the improved construction justdescribed a considerable saving in paper is eflected over thoseconstructions in which the paper is wrapped spirally about the twistedconductors due to the fact that a single strip of paper is disposedlongitudinally of the cable rather than bly in overlapping convolutionssuch as shown at l8. Due to the fact that the longitudinal wrap l4closely grips the periphery of each of the insulated conductors atwisted assembly of conductors is formed having a minimum uniformdiameter because only a single layer of the paper l4 surrounds theinsulation on each of the conductors. This makes it possible for thearmoring machine to apply an armor of minimum diameter evenly over theentire length of cable without variations in the tightness of armor onthe conductor assembly. At the same time the edges of the paper wrapencircling the conductors adequately protect them from damage during thearmoring operation. Inasmuch as the diameter of the armor is reduced toa minimum by the reduced overall diameter of the twisted conductors andpaper wrap a substantial saving is effected in the quantity of metallicarmor used.

It will be apparent from an examination of Fig. 2 that the layer ofpaper M is disposed at all times between the individual conductors.Should the conductors inadvertently become crushed together during thearmoring operations, thereby damaging the insulation on the individualconductors, the layer of paper will provide an additional insulatingmedium between the conductors capable of withstanding approximately 600volts. It has been found that the provision of this additionalinsulating means between the conductors reduces by a substantial amountthe number of rejects to be had in the commercial lengths of cable,which in the case of cables employed with voltages of lid to 600 aretested by placing a potential of 1501) volts across the conductors andbetween each conductor and the armor.

The s-shaped paper wrap constitutes a proin cylindrical form over boththe conductors.

By using the S-shaped wrap it is possible to manuiahture a cable whichwill withstand severe twisting or bending without injury to the innerinsulating and protective layer of paper or to the insulated conductorsthemselves.

In using the improved cable, a severed end of the armor is easilystripped by pulling the armor longitudinally of the cable because thecon-= volutions of armor slide easily over the plain longitudinallydisposed paper strip. This construction makes it possible to strip thecable quickly thereby saving considerable time in installing lengths ofthe cable. It is also a simple matter to remove the excess length ofpaper over the stripped end of the cable simply by tearingit ed at thepoint at which the armor was severed. It will be seen that by using alongitudinal strip of paper twisted together with the conductors toS-shaped formation in the combination with a spiral'metallic armor thatit is possible to secure an improved form of armored cable having theadvantages above described. These advantages make for better electricalcharacteristics of the cable, a reduction in the cost oi manufacture,and a. greater simplicity and saving of time in the use of the cable byskilled electricians. While the invention has been described thus far inconnection with a two conductor cable, it will be apparent that theinvention may be applied to cables employing a plurality ofconducdoctors I! and 20 together and about the single remainingconductor 2!. Cables having three conductors frequently have one of theconductors grounded or at a neutral potential. In such situations thelongitudinal paper strip is disposed between the conductors of highpotential to provide additional insulation; for example, .in the aaaaraa1 As shown in Fig. 5 the bushing 26 is of substantially cylindricaliorm'and is slightly tapered and provided with a slot 21. The bushingmay be made of insulating material such as sheet fiber. One edge of thebushing is bent inwardly to form a separating or dividing plate 28 whichextends substantially across the diameter of the cylindrical bushingforming the compartments 29 and 3d. The bushing is provided with anoverhanging head or edge 36.

In the use of the bushing it is grasped by the hand andinserted over theinsulated conductors, which may pass through the compartments Z9 and30;, and then pushed down firmly over the severed end of the armor. Thebead 3i overlies the rough severed edge of the armor and forms a smoothsurface upon which the insulated conductors may rest, while the wall ofthe bushing forms a liner for the end portion of the armor. The dividingplate 28 takes a position between the insulated conductprs andeffectively insulates them from each other.

It frequently happens that a careless workman, in severing the spiralarmor preparatory to stripping a length of the cable, will inadvertentlycut through the layers of insulation upon the inner conductors. Whenthis happens it is likely that steel slivers or filings incident tosevering of the armor will be embedded within the insulation surroundingthe individual conductors, and thus cause a short circuit todevelopbetween the individual conductors of the BX cable. In

those cases where the insulation on the individual conductors has beendamaged by the severing of construction 01' Fig. '3 either of theconductors I! or 20 may constitutethe neutral with the high potentialexisting between the remaining conductor and the conductor 2|.

In the modification shown by Fig. 4 a cable is shown having fourconductors 22, 23, 24 and 25. The conductors-are twisted in pairs aboutthe longitudinal paper strip l4 and if there is any -diflereuce inpotential between the pairs of conductors, the paper wrap is placedbetween those pairs subject to the greatest diflerence in potbntial.

v To protect the severed end of the armor from damaging the insulationon the individual conductors, an improved form of bushin s placed overthe end of the armor.

the metallic armor, the dividing plate prevents any possibility of ashort circuit occurring between the ccnductcrs at this point. Thedividing plate provides an effective continuation of that portion oithe. paper strip which passes between the individual conductors and thusforms in effect a complementary extension of'the shaped paper wrap atthat point where the paper 'wrap has been torn off in preparing thecable for wiring.

What I claim as new and desire to secure by Letters Patent oi the UnitedStates is:

1. An armored cable comprising a plurality of insulated electricconductors, a longitudinal strip of insulating material, said insulatedconductors being twisted together around said material to form anS-shaped wrap closely engaging the outer peripheries oi said conductorsand having a central portion positioned between said conductors and ahelical metallic armor closely engaging and surrounding said S-shapedwrap and in-

